The present invention relates to a sheet-shaped molding material, and more particularly, to a sheet-shaped molding material wherein both the upper and lower faces of a solid material such as glass fibers or the like have a paste-shaped material such as resin or the like thereon which is covered with carrier films which do not extend easily. The molding material may be wound up in a roll shape around a cylindrical core pipe for transportation and storage, the carrier film being adapted to prevent the sheet-shaped molding material from being bent, curved and so on in the width direction in the wound condition so as to retain a planar shape.
Conventionally, a soft sheet-shaped molding material which adheres to carrier films, a compound of paste-shaped material chiefly composed of the resin, and glass fibers retains its shape with difficulty immediately after manufacture. In particular, various problems are caused in the case where the sheet-shaped molding material continuously wound the cylindrical core pipe upon transportation and storage.
Firstly, conventional films made of polyethylene, polypropylene is used as the carrier film. This type is comparatively large in elongation percentage with respect to tensile force to be applied thereto. The carrier film is required to be strongly wound to some extent in the winding operation, since the winding section of a roll does not become truly round because of weak winding force. Thus, the carrier film is normally wound through the tensile force of 20 kg or more per meter. Upon application of such tensile force, the carrier film in contact against the compound extends, but both the end portions, also known as ear portions, of non-contact in the width direction do not extend, so that the film carrier is bent inwardly when it is wound around the core pipe A as shown in FIG. 9. Also, the film F which is in contact with the compound C is wetted in styrene which is a component of compound C so as to be extended, while the ear portion F-a of non-contact is not extended as shown hereinabove and is likewise bent inwardly as shown in FIG. 9. The so-called "ear cramp" phenomenon causes bending of both the end portions inwardly in the manner as described hereinabove, so that the central portion in the width direction is curved outwardly, and the face does not become flat as shown in FIG. 10. The curvature is not easily removed so as to restore the original shape during the use of the material after maturation. When the film is forced to be restored to become flat, the ear portions may be cut off or injured. Moreover, it is inconvenient in that the film can not be passed into an automatic cutting machine for cutting the sheet-shaped molding material during use because of the curvature of the film.
Secondly, when the film is extended because of the tensile force during the winding operation, the compound disposed near the core pipe becomes thinner, thus making it impossible to provide equal thickness.
Thirdly, as mentioned above, one roll is 150 through 160 kg at its limit, with 100 kg being normal in the use of the conventional carrier film, because the wound molding material is curved, the thickness is hard to equally retain, and so on. However, when the winding weight of one roll is small, exchanging of the roll during the molding requires more time and more labor, thus resulting in a problem of productivity. The number of rolls to be used is increased when a molding of large size is applied to be pressed even on the part of the user who manufactures the products by the use of this type of molding material. Accordingly, it is demanded that the weight of the one roll be increased. The press molding, which uses a molding material such as SMC, TMC, BMC or the like is becoming main stream, replacing the hand lay up or spray up methods requiring more labor, due to a desire to control recent higher personnel expenses. As the moldings become as large in size as a bathtub, water-proof pan, bathtub with wash place attached thereto and so on, the one piece becomes large in size, with molding material required to be wider and thicker. However, in the case of the TMC of thickness in the width direction, the weight per unit area becomes larger, and the thickness is hard to be equalized, with the material being hard to be restored when it has been curved, so that the winding method is not adopted with the TMC molding material of conventional construction. Thus, the accommodation to the sheet-shaped encasing has a problem, because the productivity is lower and the demand for larger size is hard to fulfill.
Fourthly, as the paste-shaped material immediately after the manufacturing operation is extremely soft, it may have a problem of being forced out from both ends of the carrier on both the upper and lower faces in the winding operation. Particularly, when the tensile force becomes larger, and the winding weight becomes larger, leaking from both ends increases, with the inconvenience that it becomes difficult to keep the thickness uniform in the width direction.